Downhole tools

ABSTRACT

A fluid operated apparatus in the form of a flow cap, is mounted on an end of a downhole tool or sub, which itself has a screw thread fitting to a further tool, sub or tubular. The cap provides a number of fluid flow channels arranged in a spiral pattern upon the outer surface. The handedness of the channels matches the handedness of the screw thread fitting so that fluid flow from ports in the tool or sub, acts to tighten the screw thread fitting. A water injection valve including a flow cap is described.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to connections to downhole tools used within oil and gas wells and in particular, though not exclusively, to an apparatus for use as a flow cap on a water injection valve to provide self tightening of the valve against the connection from which it is appended.

2. Description of the Related Art

In secondary recovery of oil and gas wells it is possible to use the technique of water flooding for enhanced oil recovery. This technique relies on injecting water into the reservoir and is normally undertaken using one or more water injection wells. Water injection valves are typically made up to a wireline lock or retrievable packer and run to depth. A suitable valve design comprises a body including a seat against which a poppet or other closing surface of the valve can rest. The poppet is biased towards the seat to hold the valve in a closed position. Water passed down the tubing string of a well bore will arrive at the poppet, the water pressure will work against the loading of the spring and force the poppet away from the seat. The water is then directed through ports in the poppet, whereupon it takes a convoluted path to return to a central path through the valve and exit at its base.

The present applicants have provided an improved water injection valve, as described in GB 2424428. This is illustrated in FIG. 1. The valve A is shown located on a packer B which is anchored to the casing or tubular string C present in the well bore D. On injecting water down the string C, the poppet E is forced downwards and the injected water can exit the valve through large flow ports F on the housing G. By this arrangement a high fluid flow rate is achieved with negligible pressure drop through the valve. The injected fluid rushes down the outer wall H of the housing G and off the nose J in to the bore K of the casing or string C. The housing G and nose J, have been shaped to be streamlined and offer the minimum resistance to fluid flow.

By creating large flow ports F from the removal of a majority of the housing G, the valve A has an efficient design providing negligible pressure drop through the valve. The valve A is also comparatively short in length and generally lightweight. While this reduces manufacture, storage and transportation costs, the valve can suffer from slackening from the packer, to which it is appended. This slackening is a recognized problem in all oilfield connections.

A screw thread connection is the standard connection type used in the oil and gas industry. In use within a well bore, these connections are subject to vertical loading, rotational loading, bending forces in deviated sections and the ingress of fluids and debris to the screw threads. For water injection valves and similar tools, flowing fluids at high rates through the tool causes jarring at any positions where the fluid changes direction, or the cross-sectional area in the fluid flow path is reduced. As a result, in use, high levels of vibration can be experienced by the tool which tends to back off any screw threads and can lead to the tool disconnecting itself from the string or upper tool from which it is appended.

This problem can be remedied for screw thread connections within the tools themselves. During assembly of the tool it is common to use a thread locking solution such as Loctite® and/or to incorporate set screws arranged perpendicularly to the central axis of the tool. Unfortunately, if the tool is supplied as a single item, it will be a third party who connects the tool to another tool or part of a string. These third parties may be deck hands or riggers, whose priority is to run the tools into the well bore as quickly as possible and will not make it a priority to ensure the threaded connections are all tightened carefully with Loctite® applied.

SUMMARY OF THE INVENTION

It is therefore an object of the present invention to provide an apparatus for use on a downhole tool which is screw threaded to a further tool or string and assists in preventing back off of the screw thread during use of the tool.

It is a further object of the present invention to provide apparatus for use on a downhole tool which causes the tool to be self tightening.

It is a further object of at least one embodiment of the present invention to provide a water injection valve which includes apparatus to assist in preventing back off of the screw thread to the anchor packer or lock to which the valve is fitted.

According to a first aspect of the present invention there is provided fluid operated apparatus for use on a downhole tool or sub which has a screw thread on an upper end thereof for connection to a further tool, sub or tubular from which it is appended, the apparatus having an outer surface upon which is arranged one or more fluid flow channels, each channel having a fluid inlet arranged at an upper end and a fluid outlet arranged at a lower end, distal from the screw thread, and each channel being formed as a portion of a spiral having a handedness, the handedness being the same as the screw thread at the upper end.

In this way, fluid entering the channels will urge the apparatus to turn in a direction with the screw thread and thereby cause tightening of the screw thread.

Those skilled in the art will be aware that screw threads provide a continuous spiral upon a surface, with the direction of the spiral defining a right handedness or left handedness of the screw thread. Thus for a right handed screw thread on the upper end and channels having a right handedness, the fluid entering the channels will urge the apparatus in a clockwise direction.

The apparatus may be considered as a male connector with the upper end considered as a female connector. Alternatively the upper end may also be a male connector.

Preferably the one or more channels are each formed as a portion of a helix on the outer surface. Such an arrangement provides a high flow rate through the channels. Each channel need not circumnavigate the outer surface and may appear as being skewed with respect to a central axis through the apparatus, with the skew direction matching the direction of the screw thread at the upper end.

Preferably there are a plurality of channels equidistantly spaced around the outer surface. This arrangement balances the applied fluid force around the apparatus.

Preferably the apparatus comprises a substantially cylindrical body with the channels arranged along a substantial length of the body. Advantageously the apparatus includes a bull nose at an end thereof. Such a bull nose provides a streamlined path for fluid exiting the channels.

Preferably each channel is separated from an adjacent channel by a channel wall. More preferably a width of the channel wall is less than a width of the channel. Advantageously, the width of the channel is substantially the same along it's length.

Preferably the tool or sub includes one or more ports arranged to provide fluid flow adjacent to the inlets of the channels. Advantageously the ports direct a substantial component of the fluid flow in a direction parallel to the central axis. Preferably the tool is an injection valve appended from a wireline lock or packer.

According to a second aspect of the present invention there is provided a method of self tightening a screw thread on a string, tool or sub in a well bore, comprising the steps:

-   -   a) locating upon the string, tool or sub an apparatus according         to the first aspect;     -   b) running the string, tool or sub into the well bore;     -   c) with the string, tool or sub positioned in the well bore,         causing fluid flow to enter the channels, the direction of fluid         flow being non-parallel to the handedness of the channels;     -   d) using fluid pressure created in the channel to urge the         apparatus to turn in a direction matching the handedness of the         screw thread on the string, tool or sub and thereby tighten the         screw thread.

In this way, the screw thread is prevented from slackening off without having to rotate the string, tool or sub in the well bore.

Preferably the tool is an injection valve and the fluid flow is injected fluid traveling through the valve in a downhole direction.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the present invention will now be described, by way of example only, with reference to the following drawings of which:

FIG. 1 is a cross-sectional view through a prior art injection valve;

FIGS. 2( a)-(d) are a flow cap according to an embodiment of the present invention in (a) 3D image, (b) plan view; (c) cross-sectional view on section line A-A of (d) cross sectional view; and

FIG. 3 is a cross-sectional view through an injection valve including the flow cap of FIG. 2.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Reference is made to FIGS. 2( a)-(d) which illustrate apparatus in the form of a flow cap, generally indicated by reference numeral 10, according to an embodiment of the present invention. Cap 10 comprises a substantially cylindrical body 12 having a tapered or bull nose 14 at a forward end 16. On an outer surface 18 of the body 12 there are located nine channels 20. Each channel 20 is skewed with respect to a central axis 22 through the cap 10. The channels lie on a portion of a helix and can be considered as right handed.

The cap 10 is arranged to be secured upon a downhole tool or sub via a threaded inner recess 24 and apertures 26 a,b for set screws, to mechanically secure the cap 10 to the tool or sub. The direction of skew of the channels i.e. left or right handed, is selected to be the same as the screw thread fitting of the tool or sub onto a further tool sub or tubular located above. Indeed the thread at recess 24 has the same handedness as the channels also.

The nine channels 20 are arranged equidistantly around the outer surface 18. Each channel 20 has a uniform width so that the path of each channel 20 describes a helix. The channels therefore appear to spiral around the body 12. In the embodiment shown each channel 20 rotates around the body 12 by 27 degrees along its' length.

Neighbouring channels 20 are separated by a wall 28. Each wall has a width which is appreciably thinner than the width of the channels on either side. This allows for maximum flow through the channels 20. The height of each wall tapers towards the outer surface 18 at each end 32 a,b.

In the embodiment shown a central bore 34 is located on the central axis through the cap 10. Such a fluid passageway from the outer surface 18 to the recess 24 prevents a pressure differential being created across the cap 10.

In use, referring now to FIG. 3, flow cap 10 is attached to a downhole tool or sub, in this example a water injection valve 40 is illustrated. A tubular portion 42 of the valve 40 is screw threaded into the recess 24. The cap 10 is fixed to the portion 42 by inserting set screws through the connections 26. These connections are perpendicular to the central axis 22 and are not affected by fluid flow passed the cap 10.

As illustrated on FIG. 1, the valve 40 is connected to a wireline lock or packer via the right handed screw thread 44 located at an upper end 46 of the valve 40. The valve 40 and wireline packer are run into a casing or production tubing on a wireline. At a desired location, the packer is set to lock the valve 40 in a position in the tubing. Fluid flow in the tubing from above, created by increasing the pump pressure at surface, opens the valve 40. Fluid pressure acts on the poppet 48 in the valve 40 and the poppet is pushed down against the spring 50. The poppet is released from the seat 52 and injected fluid flows out of the valve 40 through large ports 54 located around the valve housing 56.

At a lower end 58 of the valve 40, the diameter of the valve 40 is reduced. At the point where the diameter decreases, the flow ports 54 open across the reduction 60. As a result fluid flow at the reduction 60 becomes parallel to the central axis 22. The flow cap 10 is sized such that the diameter of the body 12 is approximately equal to the diameter of the valve 40 after the reduction 60. In this way fluid flowing from the ports 54 parallel to the central axis 22, will enter the channels 20.

As the channels 20 are skewed with respect to the axis 22, fluid impacts the wall 28 between the channels 20. On impact the flow cap is urged to travel in clockwise direction as the channels are right handed. As the cap 10 is urged in a clockwise direction, this movement is transmitted through the valve 10 to the screw thread 44. Movement of the screw thread 44 in a clockwise direction tightens the connection between the valve 40 and the wireline packer. Thus, in the event that the water pressure through the valve causes vibrations which would tend to slacken the connection 44, the connection 44 is urged to remain tightened by fluid pressure moving the flow cap 10.

The apparatus of the present invention is not designed to over torque the screw thread connection. It is generally designed merely to urge the connection to remain in position and prevent the connection loosening and slackening off.

It should be noted that the apparatus works with the tool or sub held in a stationary position with drive being supplied entirely by fluid flow within the channels. This is in contrast to tools located on drill strings such as a drill bit. In such arrangements the apparatus is driven to rotate by rotation of the string at the surface of the well. Connections in the string have a screw thread in an opposite direction to the rotation of the string so that the connections are not released in use. However, as the string is forceably rotated, in the event that the tool sticks in the well bore, the connections can be over-torqued and shear the threads. This does not occur in the present invention which merely assists in preventing slackening of the connection.

It is thus a principle advantage of the present invention to provide a fluid operated apparatus for use on a downhole tool or sub which has a screw thread on an upper end thereof for connection to a further tool, sub or tubular from which it is appended, which assists in preventing back off of the screw thread during use of the tool.

It is a further advantage of the present invention to provide a fitting for use on a downhole tool which causes the tool to be self tightening.

It is a yet further advantage of at least one embodiment of the present invention to provide a water injection valve which includes a flow cap to assist in preventing back off of the screw thread to the anchor packer or lock to which the valve is fitted.

It will be appreciated by those skilled in the art that various modifications may be made to the invention herein described without departing from the scope thereof. For example, the apparatus may be formed as a sub within a string or tubular and does not require to be located at an end of a tool. Alternatively the channels could be machined directly on to the outer surface of a tool. Additionally while an injection valve is described, any tool which provides fluid flow ports could benefit from the present invention, for example, a circulation tool could be used. 

1. A fluid operated apparatus for use on a downhole tool or sub comprising, a screw thread formed on an upper end thereof for connection to a further tool, sub or tubular from which it is appended, the apparatus having an outer surface upon which is arranged one or more fluid flow channels, each channel having a fluid inlet arranged at an upper end and a fluid outlet arranged at a lower end, distal from the screw thread, and each channel being formed as a portion of a spiral having a handedness, the handedness being the same as the screw thread at the upper end.
 2. A fluid operated apparatus according to claim 1 wherein the apparatus is a male connector with the upper end being a female connector.
 3. A fluid operated apparatus according to claim 2 wherein the upper end is also a male connector.
 4. A fluid operated apparatus according to claim 1 wherein one or more channels are each formed as a portion of a helix on the outer surface.
 5. A fluid operated apparatus according to claim 1 wherein there are a plurality of channels equidistantly spaced around the outer surface.
 6. A fluid operated apparatus according to claim 1 wherein the apparatus comprises a substantially cylindrical body with the channels arranged along a substantial length of the body.
 7. A fluid operated apparatus according to claim 1 wherein the apparatus includes a bull nose at an end thereof.
 8. A fluid operated apparatus according to claim 1 wherein each channel is separated from an adjacent channel by a channel wall.
 9. A fluid operated apparatus according to claim 8 wherein a width of the channel wall is less than a width of the channel.
 10. A fluid operated apparatus according to claim 9 wherein the width of the channel is substantially the same along its length.
 11. A fluid operated apparatus according to claim 1 wherein the tool or sub includes one or more port arranged to provide fluid flow adjacent to the inlets of the channels.
 12. A fluid operated apparatus according to claim 1 wherein the tool is an adjacent valve appended from a wireline lock or packer.
 13. A method of self tightening a screw thread on a string, tool or sub in a well bore, comprised the steps: a) locating upon a string, tool or sub an apparatus according to claim 1; b) running the string, tool or sub into the well bore; c) with the string, tool or sub positioned in the well bore, causing fluid flow to enter the channels, the direction of the fluid flow being non-parallel to the handedness of the channels; d) using fluid pressure created in the channel to urge the apparatus to turn in direction matching the handedness of the screw thread on the string, tool or sub and thereby tightening the screw thread.
 14. A method according to claim 13 wherein the tool is an injection valve and the fluid flow is injected fluid travelling through the valve in a downhole direction. 